1. Field of the Invention
The invention pertains to data transmission in a wireless radiocommunication system comprising a plurality of antennas. It relates to a method of positioning the antennas of the system.
Known among wireless communication systems are data transmission systems with plural antennas operating inside buildings, indoor areas, or operating in semi-enclosed areas. These communication systems are generally composed of a base station and of several mobile terminals. Standards such as Hiperlan2 and IEEE802.11a define such communication systems operating in frequency bands situated in the vicinity of 5 GHz.
Such systems also find an application in high-definition wireless cameras.
The quality of the data transmission between base station and mobile terminals depends mainly or particularly on the antenna system used for the emission and the reception of the data. The energy transmitted during reception must be maximized so as to render the link effective and reduce the energy demands, a significant point for any user not having a fixed energy source. This is why the optimization of the reception by antennas is a significant point in the development of transceivers.
To increase the resistance to noise and to echos of these transmission systems, it is known to diversify the antennas, that is to say to carry out MRC (standing for Maximum Ratio Combining) multiantenna processing. The antenna diversity consists in multiplying the number of antennas and therefore the transmission paths of the waves so that the antennas are not subject to the same echo constraints and in combining the signals received from the various antennas. It therefore allows better stability by eradicating the untimely fading which often characterizes single-antenna solutions.
Among the antenna techniques also used to increase the range of a radio system, sectorization is certainly one of the most widespread. It consists in having available several beams each affording a different angular coverage. The radio system adjusts the choice of the sector as a function of the position of the emission and reception equipment.
2. Description of the Prior Art
These two techniques, that is to say antenna diversity and sectorization, are not antinomic. Specifically, known from document US 2004/0196834 is a system for wireless transmission comprising a plurality of antennas with sectorization in such a way that the transmission of the data is effected by at least one selected antenna sector. At each new selection, a new antenna sector is chosen and an instantaneous toggling takes places. This signifies that the radio link passes from one sector of an antenna to another sector of another antenna abruptly. This abrupt transition gives rise to a major risk of occurrence of error and possibly the momentary loss of the link.
To remedy this problem the invention proposes that the signals received by the assembly of antennas be combined, whatever the sector to which they belong.